The Radiation Assessment Detector (RAD) on the Curiosity rover has been characterizing the Martian surface radiation field since 2012. The dose observed by RAD is influenced by a variety of factors, including an essential one, the terrain. After parking near Murray Buttes in September 2016 where it first detected a similar to 5% decrease in dose rate, the rover has passed a series of other interesting terrains where we find decreases in the dose rate reaching 19%. This radiation reduction is due to extra shielding provided by the nearby surface structure, confirming the potential use of surface structures for radiation protection of humans on Mars. Combining a zenith-angle-dependent radiation model and the rover panoramic visibility map we calculate the downward radiation dose that RAD should observe under different topographic shielding conditions. This allows us to further evaluate the terrain-generated albedo dose at different locations. We finally estimate that on a flat surface the albedo radiation is between similar to 18% and 24% of the total surface dose. This study contributes to developing a realistic terrain-based radiation map which is important for future Mars explorers.

Abstract Wrinkle ridges are widespread compressional tectonic features on Mars and are important records of the planet's global contractional history. However, their formation, evolution and subsequent modification by other geologic processes remain poorly constrained. Combining radar data, elevation data and high‐resolution imagery, we find that the uppermost layer of the Late Amazonian volcanic (lAv) unit is ∼50 m thick and exhibits dielectric properties consistent with porous basalt ( = 7.50 ± 0.69; = 0.011–0.077). Stratigraphic analyses and crater dating within the Amazonis Planitia west of Olympus Mons reveal multiple resurfacing events at ∼1.3 Ga, ∼240 Ma, and ∼28 Ma. The estimated volume of the youngest flow is ∼7.50 × 10 4 km 3 , and flow thicknesses appear to have progressively decreased over time. Radar and image data demonstrate that the latest lava flow completely buried the preexisting ridges while preserving their subsurface geometry. Wrinkle ridges within the lAv unit differ from global averages, showing enhanced widths, lower heights, larger width‐to‐height ratios, and reduced elevation offsets. These morphometric deviations suggest substantial post‐formational modification by volcanic flooding, topography inflation and sedimentation with potential contributions from varying fault geometry and slip. The modification may have led to an underestimation of derived strain by up to ∼22%. These findings reveal that volcanism both alters surface ridge topography and preserves underlying structure, emphasizing the necessity of radar constraints to reconstruct tectonic history on Mars.

Landslides are globally distributed on Mars and resemble terrestrial analogues in morphology. Understanding the spatial distribution of Martian landslides provides key constraints on Martian surface processes, tectonic activity, and the environmental conditions that govern landslide mechanics. However, existing global inventories remain incomplete because capturing small, overlapping, or morphologically ambiguous deposits solely relying on manual mapping is challenging, leaving uncertainty in understanding their spatial distribution. In this study, we propose Mars-DiSVM, a landslide identification framework based on multimodal images, which fuses features extracted from optical, thermal, and topographic data using a DINOv2 backbone, and the features are classified by a downstream Support Vector Machine (SVM) classifier. The framework using concatenated feature representation achieved a classification accuracy of 97.5%. Applying Mars-DiSVM to four areas of interest (AOIs), 25 previously unmapped, small-scale landslides have been identified over an area of 224,676 km ^2 . These landslides are clustered within impact craters and along valley slopes, where manual mapping commonly underrepresents small deposits. Three of the landslides occur in close proximity to impact craters, implying impact as a possible trigger. The results demonstrate the potential of the framework to refine the global landslide inventory on Mars. The expanded inventory produced by Mars-DiSVM reveals that small landslides constitute a substantial and previously underrepresented component of Mars mass wasting, providing critical constraints on landslides occurrence and triggering mechanism and offering new opportunities to reassess Martian surface activity and crater degradation processes.

Liquid water exists on the Earth and several other planetary bodies in our solar system. The chemical character of these aqueous reservoirs is central to evaluating their habitability. Here, we synthesize the chemical features of water reservoirs and their biological implications on the modern Earth. We then outline constraints on the evolutionary history of Earth's ocean chemistry and discuss its interplay with the biosphere. Furthermore, we examine the inferred chemical environments of water bodies on early Mars, dwarf planet Ceres, Jupiter's moon Europa and Saturn's moons Enceladus and Titan. We conclude by outlining priority questions for future planetary habitability studies.

Manganese oxides, thought to form almost exclusively through reactions between Mn2+ and O2, catalyze oxidative transformations among redox-sensitive metals. Thus, the occurrence of Mn oxides, either observed or inferred from sedimentary geochemical data, has formed the basis for multiple hypotheses concerning the evolution of the atmospheric redox state on the early Earth and Mars. Here, using theory and experiments, we report that the band gap of common Ca/Mg carbonate minerals (including calcite, magnesite, and aragonite) is significantly lowered by trace incorporation (0.8 wt% or lower) of Mn(II) into their bulk structure or surface, conferring photochemical reactivity under ultraviolet conditions relevant to early Earth and Mars (200 to 400 nm). Moreover, we show that surface incorporation of Mn(II) reduces the fundamental band gap much more effectively (by >1 eV) than bulk incorporation. Our results suggest that photo-oxidation of Mn(II)-bearing carbonates could have occurred widely on planetary surfaces, resulting in the abiotic formation of manganese oxides without free molecular oxygen. Photochemically driven redox cycling of manganese could help sustain redox disequilibria for microbial metabolisms, but compromises the use of manganese oxides as oxygen barometers.

Tyrrhena Terra, a region located in the cratered highlands between Hellas and Isidis Planitia on Mars, is distinguished by its extensive presence of hydrated minerals. Using 542 hyperspectral images from the Compact Reconnaissance Imaging Spectrometer for Mars, we detected 252 exposures of hydrated minerals. This region is characterized by a widespread distribution of Fe/Mg-smectites/vermiculites and chlorite, with additional detections of Al-phyllosilicates, zeolites, prehnite, hydrated silica, and carbonates. We classified the mineralogical detections in classes of impact crater diameters, locations in craters, and for those > 20 km, their relative degradation stages. We found that craters < 10 km display a lower mineral diversity than larger ones. In contrast, craters > 20 km display a high mineral diversity, especially in central peaks, suggesting a strong influence of hydrothermal processes and deep excavation. Among this diameter range, fresh, young craters exhibit a much higher mineral diversity than degraded, old craters. Fe/Mg-phyllosilicates are dominant in the latter, as well as in sedimentary units of topographically low areas. These results indicate a long-term alteration cycle in the most ancient period, where the initial, diverse hydrated minerals-formed through exhumation and/or hydrothermal circulation within large impacts-were subsequently transformed by surface weathering and/or buried, dissolved, or eroded away by other post-impact processes, then transported and deposited in lowlands by fluvial erosion. Although Tyrrhena Terra is dominated by impact-related hydrated mineral detections, our study shows that the overprint of Noachian age weathering is visible within these detections.

The oxygen fugacity (hereafter referred as fO(2)) of terrestrial planets is key in defining the outcome of planetary-scale differentiation and the planets' potential habitability. Reconstructing the initial fO(2) records in the mantle right after core formation for terrestrial planets remain challenging due to frequent secondary modifications. Here, we show based on studies of ureilites and diogenites that measurable Ti isotope fractionation occurred during melt extraction from planetary mantle in the presence of Ti3+, and demonstrate that Ti isotopes can serve as a fO(2) tracer of planetary mantle reservoirs. We also show a positive correlation between the Ti-49/Ti-47 and La/Yb ratios for shergottites, which, when integrated with chronological constraints, imply the occurrence of Ti isotope fractionations arising from the presence of Ti3+ during early mantle differentiation of Mars. Further constraints define reducing conditions of similar to Delta IW-0.8 to similar to Delta IW-1.6 for early-formed martian mantle reservoirs at similar to 4.5 Ga. This fO(2) estimate coincides with the lowest recommended values from martian meteorites, that of core-mantle differentiation for Mars and of diogenites, but is more oxidizing than that of ureilites. Mantle outgassing under these conditions would result in a reducing primordial atmosphere that is in stark contrast with Mars' current CO2-dominated atmosphere.

Exploring the presence and behavior of water on Mars is critical for understanding the planet’s geological evolution, hydrological processes, and potential habitability, which has been a central objective of past and ongoing Martian exploration missions. Martian geomorphology provides evidence of ancient groundwater activity, but confirmation of present-day liquid water remains limited. Here, we infer near-surface brines confined to meter-scale depths in regions north of about 30 °N in the northern hemisphere, based on the analysis of seasonal variations in marsquake seismicity and thermal modeling. The absence of seasonal marsquakes during colder periods and their abrupt resurgence in warmer seasons can be explained by ice-to-brine phase transitions. Our findings reveal a mechanism whereby seasonal melting of subsurface ice elevates pore pressure and lubricates faults, leading to a reduction in frictional strength, and ultimately inducing marsquakes. This mechanism accounts for the seasonal variation, clustering, high seismic b-values, and shallow focal depths of seasonal marsquakes. Additionally, we estimate that the melting point of briny ice on Mars is below approximately 250 ± 13 K, advancing our understanding of Mars’ present-day brine cycle and near-surface hydrological processes. The study finds that seasonal marsquake patterns may indicate active near-surface brines on Mars today. By connecting seismicity changes to ice-to-brine melting, it infers that shallow liquid water continues to operate beneath the surface and influence Martian fault activity.

Introduction Impact craters are widely used to investigate the geologic history of planetary surfaces. For example, their morphology bears clues on past surfaces processes that affected the surface such as erosion, sedimentary deposit and volcanic processes. One of the most interesting use of impact craters is the dating of planetary surfaces using their size frequency distribution (Hartmann and Neukum 2001; Stöffler and Ryder 2001; Young 1940). This method has been used in almost every study that provide an age for geologic bodies other than Earth.If lunar crater size frequency distributions are most often pristine, craters on many other bodies are degraded over time. Hence crater size frequency distributions often present a depletion of small craters compared to the lunar ones. Mars is a good example of this phenomenon that has been named Opik effect (Opik 1966). Taking into account crater degradation when dating planetary surface will not only improve this method, but also provides new insights into the geological processes which resulted in the crater degradation.In this study we combine statistic and morphology of craters in order to investigate the timing and intensity of surface processes. We introduce the notion of crater size and depth frequency distributions, adding a dimension to classic size and depth frequency distribution. Using crater chronology models, those crater size and depth frequency distributions can be interpreted in term of crater depth depletion speed that we refer as crater obliteration. Method Craters populations are already widely referenced. On Mars, Robbins & Hynek, 2012 proposed a huge crater database that they estimate complete down to 1 km of diameter. In this database, most craters above 6 km of diameter are provided with a morphology. We computed crater depth from the elevation of the floor and the median elevation of the rims.Crater size and depth frequency distribution are then constructed using probability density distribution as recommended by Robbins et al., 2018. Each crater is convoluted by a 2D gaussian determined by the analytical error on the measured depth and diameter.Assuming that the deepest craters are the freshest ones, we used crater chronology models (Ivanov 2001; Neukum, Ivanov, and Hartmann 2001) to associate a depth for each diameter and age (Figure 1). For each diameter, we then derivate depth according to age to compute obliteration.We observe strong noise at the limit of the distribution, that cause an increase in computed obliteration for recent ages. This is caused by the spreading of the crater size and depth frequency distribution beyond the observed craters as a result of convolution. To remove this bias, we only keep obliterations measured when the model number of crater is more than 5. Results From Robbins & Hynek, 2012 crater databases, we computed crater size and depth frequency distribution for geologic areas of Mars simplified from the geologic map of Tanaka et al., 2014. We computed obliteration rates from thoseWe presents here the obliterations rates obtained for 3 Martian geologic areas, namely the Southern Highland, Tharsis Province and the Hesperian lowlands, that illustrate our main results.Only the most cratered surfaces, such as the Southern Highlands present a number of craters large enough to investigate Noachian obliteration rates (Figure 2). During this era, obliteration rates reach several thousands m/Gy, but rapidly decrease during early Hesperian and are close to 0 during Amazonian.Volcanic provinces such as Tharsis, Isidis and Elysium present obliterations rates more important than the rest of the planet during Hesperian. This suggest that our method is sensitive to volcanic activity. We show here the example of the province of Tharsis (Figure 3), where obliteration rates decreased slower than on the rest of the planet, suggesting a persistence of volcanic activity until early Amazonian.Northern lowlands witness Amazonian obliteration rates one order of magnitude higher than the rest of the planet (Figure 4). This observation is still under further investigation, but may suggest a continuous emplacement of geologic material during middle Amazonian which may be related to Vastitas Borealis Formation.We have developed a new method to model crater distribution and degradation taking into account of the size and depth of impact craters. Using this model, we were able to retrace the variations of crater obliteration through Martian era, and provide insight into the geological processes dominating crater degradation. The method with additional inputs from crater depths provides novel insights into the geological processes dominating crater degradation at different epochs in Martian history. Combined with higher resolution datasets, this method has potential to be applied to understand regional geological processes on Mars and other planetary bodies. BibliographyHartmann, William K., and Gerhard Neukum. 2001. “Cratering Chronology and the Evolution of Mars.” Space Science Reviews 96(1–4): 165–94.Ivanov, Boris A. 2001. “Mars/Moon Cratering Rate Ratio Estimates.” Space Science Reviews (November 2000).Neukum, Gerhard, Boris A. Ivanov, and William K. Hartmann. 2001. “Cratering Records in the Inner Solar System in Relation to the Lunar Reference System.” Space Science Reviews 96(1–4): 55–86.Opik, E. J. 1966. “The Martian Surface.” Science 153(3733): 255–65. http://www.sciencemag.org/cgi/doi/10.1126/science.153.3733.255.Robbins, Stuart J. et al. 2018. “Revised Recommended Methods for Analyzing Crater Size-Frequency Distributions.” Meteoritics and Planetary Science 53(4): 891–931.Robbins, Stuart J., and Brian M. Hynek. 2012. “A New Global Database of Mars Impact Craters ≥1 Km: 1. Database Creation, Properties, and Parameters.” Journal of Geophysical Research E: Planets 117(5): 1–18.Stöffler, D., and G Ryder. 2001. “Stratigraphy and Isotope Ages of Lunar Geologics Units: Chronological Standard for the Inner Solar System.” : 9–54.Tanaka, Kenneth L. et al. 2014. “Geologic Map of Mars.” USGS.Young, J. 1940. “A Statistical Investigation of Diameter and Distribution of Lunar Craters.” Journal of the British Astronomical Association.

The Mars Science Laboratory has been investigating the central mound of Gale crater since 2012 and revealed evidence of silica enrichment in several locations, suggesting that the geologic processes related to the formation of hydrated silica could be widespread. A reanalysis of orbital data over Aeolis Mons indicates the existence of an extensive unit rich in hydrated silica. These silica-enriched deposits, found at the base of Aeolis Mons, span elevations from -4513 m to -3351 m. The mapped hydrated silica deposits are spatially adjacent to an erosion-resistant capping unit, previously mapped as the mound skirting unit, which lies beneath the terminal deposits from local canyons and valleys. We hypothesize that the hydrated silica-bearing unit precipitated from groundwater which migrated upwards or deposited as a volcaniclastic silica-rich layer which was rehydrated during the late-stage canyon and valley forming events. The silica-bearing unit beneath the capping unit is protected against erosion by younger fan-shaped deposits and became exposed only recently. The mineralogy and stratigraphic relations with Mount Sharp units imply that the aqueous activities leading to silica diagenesis were likely a basin-wide process that occurred long after the formation of lakes in Gale crater's geological history and experienced limited water-rock interaction since then.

Abstract H2 in a CO2 atmosphere may serve as a potential solution to the early Mars climate paradox, but its unknown sources cast doubts on the proposed mechanism. Impact cratering is an energetic process that may modify the surface redox budget. Here, we investigate the potential influence of impact‐related melt oxidation and serpentinization on global climate conditions. We show that impact melt and the projectile's significant oxidizing potential during basin‐forming impacts (Basin size ≥1,250 km) result in sufficient H2 to raise the global mean temperature to above 273K, which lasts for up to 105 − 106 yr considering rate‐limited regime. Impact‐induced serpentinization has limited consequences on the global climate in comparison. Episodic warming after large impacts may have enabled the presence of liquid water for up to several million years in the Noachian, resulting in the chemical evolution of the planet's surface co‐evolving with the planetary atmosphere in an episodic manner.

The Zhurong rover of the Tianwen-1 mission landed in southern Utopia Planitia, providing a unique window into the evolutionary history of the Martian lowlands. During its first 110 sols, Zhurong investigated and categorized surface targets into igneous rocks, lithified duricrusts, cemented duricrusts, soils and sands. The lithified duricrusts, analysed by using laser-induced breakdown spectroscopy onboard Zhurong, show elevated water contents and distinct compositions from those of igneous rocks. The cemented duricrusts are likely formed via water vapor-frost cycling at the atmosphere-soil interface, as supported by the local meteorological conditions. Soils and sands contain elevated magnesium and water, attributed to both hydrated magnesium salts and adsorbed water. The compositional and meteorological evidence indicates potential Amazonian brine activities and present-day water vapor cycling at the soil-atmosphere interface. Searching for further clues to water-related activities and determining the water source by Zhurong are critical to constrain the volatile evolution history at the landing site.

Abstract Knowledge of Martian crust and uppermost mantle aid us studying the planet's evolution. NASA's InSight mission provides seismic data being used to reveal the interior structure. Most studies have focused on the crustal structure beneath InSight lander, but the seismic structure of other regions has remained poorly known. We use surface‐wave data to investigate the crustal structure of a large region along the Medusa Fossae Formation and the dichotomy. We adopt the largest‐magnitude marsquake (S1222a) that has been recorded, which provides both Rayleigh‐ and Love‐wave signals. We measure and jointly invert these surface‐wave fundamental‐mode group velocities from ∼15 to 40 s to estimate the average 1D isotropic velocity models. These models includes a high‐velocity layer at ∼7‐km depth, which could be due to a regional basaltic activity or regional stress. Our models also indicate that a common intra‐crustal structure (∼12–40 km depth) may exist in this region along the dichotomy.

Earth’s mantle has a two-layered structure, with the upper and lower mantle domains separated by a seismic discontinuity at about 660 km (refs. 1 , 2 ). The extent of mass transfer between these mantle domains throughout Earth’s history is, however, poorly understood. Continental crust extraction results in Ti-stable isotopic fractionation, producing isotopically light melting residues 3 – 7 . Mantle recycling of these components can impart Ti isotope variability that is trackable in deep time. We report ultrahigh-precision 49 Ti/ 47 Ti ratios for chondrites, ancient terrestrial mantle-derived lavas ranging from 3.8 to 2.0 billion years ago (Ga) and modern ocean island basalts (OIBs). Our new Ti bulk silicate Earth (BSE) estimate based on chondrites is 0.052 ± 0.006‰ heavier than the modern upper mantle sampled by normal mid-ocean ridge basalts (N-MORBs). The 49 Ti/ 47 Ti ratio of Earth’s upper mantle was chondritic before 3.5 Ga and evolved to a N-MORB-like composition between approximately 3.5 and 2.7 Ga, establishing that more continental crust was extracted during this epoch. The +0.052 ± 0.006‰ offset between BSE and N-MORBs requires that <30% of Earth’s mantle equilibrated with recycled crustal material, implying limited mass exchange between the upper and lower mantle and, therefore, preservation of a primordial lower-mantle reservoir for most of Earth’s geologic history. Modern OIBs record variable 49 Ti/ 47 Ti ratios ranging from chondritic to N-MORBs compositions, indicating continuing disruption of Earth’s primordial mantle. Thus, modern-style plate tectonics with high mass transfer between the upper and lower mantle only represents a recent feature of Earth’s history.

SUMMARY The horizontal-to-vertical (H/V) spectral ratio inversion is a traditional technique for deriving the local subsurface structure on Earth. We calculated the H/V from the ambient vibrations at different wind levels at the InSight landing site, on Mars, and also computed the H/V from the S-wave coda of the martian seismic events (marsquakes). Different H/V curves were obtained for different wind periods and from the marsquakes. From the ambient vibrations, the recordings during low-wind periods are close to the instrument self-noise level. During high-wind periods, the seismic recordings are highly contaminated by the interaction of the lander with the wind and the martian ground. Therefore, these recordings are less favourable for traditional H/V analysis. Instead, the recordings of the S-wave coda of marsquakes were preferred to derive the characteristic H/V curve of this site between 0.4 and 10 Hz. The final H/V curve presents a characteristic trough at 2.4 Hz and a strong peak at 8 Hz. Using a full diffuse wavefield approach as the forward computation and the Neighbourhood Algorithm as the sampling technique, we invert for the 1-D shear wave velocity structure at the InSight landing site. Based on our inversion results, we propose a strong site effect at the InSight site to be due to the presence of a shallow high-velocity layer (SHVL) over low-velocity units. The SHVL is likely placed below a layer of coarse blocky ejecta and can be associated with Early Amazonian basaltic lava flows. The units below the SHVL have lower velocities, possibly related to a Late Hesperian or Early Amazonian epoch with a different magmatic regime and/or a greater impact rate and more extensive weathering. An extremely weak buried low velocity layer (bLVL) between these lava flows explains the data around the 2.4 Hz trough, whereas a more competent bLVL would not generate this latter feature. These subsurface models are in good agreement with results from hammering experiment and compliance measurements at the InSight landing site. Finally, this site effect is revealed only by seismic events data and explains the larger horizontal than vertical ground motion recorded for certain type of marsquakes.